The toxic properties of cadmium compounds have been well recognized in many species. There is little evidence to suggest a physiologic role for the metal. Rather, because of its long biologic half-life, cadmium acts as a cumulative poison, and even at quite low ambient concentrations, it can accumulate in mammals to values not insignificant in terms of critical toxic levels. The problem of cadmium toxicity has become especially important, as cadmium concentrations in the environment have begun to rise owing to a variety of human activities such as mining, the metallurgical industry, coal combustion, and the use of cadmium-containing fertilizers. It seemed appropriate, therefore, to assemble in one volume an up-to-date analysis of the mechanism of action of cadmium on biologic systems. Aspects of this field have repeatedly been reviewed in the past, and particular reference must be made to the volumes prepared by FRIBERG and collaborators from Sweden. Much outstanding work on cadmium has also been reported from Japan, and I am happy that investigators from both countries were able to contribute to the present volume. Obviously, this volume does not report a consensus by its contributors. The purpose of the work was to permit leading investigators in the field to present a critical review with sufficient documentation to support their interpretations and conclusions. A certain amount of overlap and disagreement between chapters was therefore unavoidable. The result, I hope, will be a useful state-of-the-art discussion.